1. Field of the Invention
The present invention relates to a developing device for an electrophotographic image forming apparatus which develops an electrostatic latent image formed on a photosensitive medium using developer. More particularly, the present invention relates to a developing device having an improved sealing structure for preventing developer from leaking.
2. Description of the Related Art
Referring to FIG. 1, in an electrophotographic image forming apparatus such as a laser beam printer, an electrostatic latent image formed on a photosensitive medium 20 by a laser scanner 40 is developed into a visible image by a developing device 10 using developer, and then, the developer image is transferred onto a sheet of paper 1. That is, when the laser scanner 40 scans the laser onto a surface of the photosensitive medium 20 that is charged to a predetermined electric potential by a charger 30, the electric potential of the exposed surface is lowered and an electrostatic latent image is formed. Developer particles attached on a developing roller 11 of the developing device 10 are transferred onto the electrostatic latent image by an electric force to develop the image.
The developing device 10 includes an agitator 14 for agitating the developer in a housing 15 of the developing device 10 to electrically charge the developer by friction, a supplying roller 13 for supplying the charged developer onto a surface of the developing roller 11, and a blade 12 for controlling a thickness of the developer layer attached on the surface of the developing roller 11. Therefore, the developer particles charged by the agitator 14 are supplied to the surface of the developing roller 11 by the supplying roller 13, and the blade 12 maintains a constant thickness of developer attached on the developing roller 11. Then, the developer particles are attached onto the electrostatic latent image on the photosensitive medium 20 separated from the developing roller 11 by a developing gap (g). Bias voltages are applied to the supplying roller 13, the developing roller 11, and the photosensitive medium 20 for transferring the charged developer particles.
Referring to FIG. 2, a sealing member 16 for preventing the developer particles from leaking out is installed between the blade 12 and an inner wall 15a of the housing 15. That is, the sealing members 16 are installed on both end portions of the blade 12 to prevent the developer from leaking through a gap between the inner wall 15a of the housing 15 and the blade 12.
However, according to the above conventional sealing structure, the developer can leak out through the gap between the sealing member 16 and the blade 12. That is, the sealing member 16 is generally formed of a sponge, and even if the sponge 16 is adhered to both ends of the blade 12, the developer particles may leak through the small gap between the sponge 16 and the blade 12 after rotating the developing roller 11. If the attaching force of the sealing member 16 to the end portion of the blade 12 is increased, leakage of the developer may be prevented. However, in this case, the blade 12 may be curved, and thus may not maintain a constant thickness developer layer on the developing roller 11. In addition, in consideration of the above problem, the both end portions of the blade 12 may be formed of a material having high rigidity and the sealing member 16 may be strongly attached to the both end portions of the blade 12 to prevent the blade 12 from curving. However, in this case, the hard portions of the blade 12 that have a high rigidity may scratch the surface of the developing roller 11, and thus, the life span of the developing roller 11 may be shortened.
Therefore, there is a need for a sealing structure for a developing device that does not damage the developing roller and can prevent the developer from leaking out.